Update mobile.html

docs/mobile.html

@@ -37,6 +37,7 @@
         <div class="artplayer-danmuku"></div>
         <p class="tip"></p>
     </div>
+    <img src="/assets/sample/test.png" style="display: none;">
     <script src="./assets/js/vconsole.min.js"></script>
     <script>var vConsole = new VConsole();</script>
     <script src="./uncompiled/artplayer/index.js"></script>